Older Australians are being encouraged to get the free pneumococcal vaccine, with research showing antibiotics fails to treat pneumonia in 20 per cent of cases.

One-in-four patients with pneumonia don't respond to antibiotics, leading to calls for older Australians to get vaccinated against a deadly strain of the serious lung infection.

A US study of 250,000 people presented at the American Thoracic Society International conference in Washington showed antibiotics failed to treat community-acquired pneumonia - that is outside of a hospital - in 20 per cent of cases.

The failure rate was worst for penicillin based antibiotics at more than 25 per cent.

Researchers at LA BioMed defined antibiotic failure when the patient either needed a second prescription, needed to go to hospital, or if their antibiotic was changed.

One of the significant predictors of antibiotic failure was having pneumococcal pneumonia, a type of bacterial pneumonia that is specifically caused by Streptococcus pneumoniae.

The research also showed that patients over the age of 65 were nearly twice as likely to be hospitalised for pneumonia compared to younger patients.

Infectious disease expert Professor Raina MacIntyre - head of the School of Public Health and Community Medicine at UNSW - says the research highlights the vital importance to close the gap between childhood and adult vaccination rates.

Despite pneumoccal pneumonia being the most common cause of community-acquired pneumonia and resistant to antibiotics, Prof MacIntyre says the uptake of the pneumoccal vaccine is immeasurably bad.

"We've got an effective vaccine that the government funds for everyone 65 and over but the uptake rate is just abysmal," said Professor MacIntyre.

About three-and-a-half million Australians aged over 65 are eligible for pneumococcal and annual influenza vaccines, but figures recently published in the Medical Journal of Australia showed only 51 per cent of them had received both vaccines.

According to Lung Foundation Australia, pneumonia is among the top 15 contributing causes of death nationally and among the top five leading causes of hospitalisation in Australia.

Professor MacIntyre says while antibiotics do help in treating pneumonia there is still a fraction of people it won't work for.

"The death rate from bacterial pneumonia has not been affected by antibiotics and it's because people tend to die very quickly."

She says without the protection of vaccination, once a person gets pneumonia their health can deteriorate very rapidly before antibiotics have a chance to work.

"The body's immune system just goes into overdrive and people can just die of overwhelming sepsis."